MTC is different from current communication models as it potentially involves very large number of communicating entities (MTC devices) with little traffic per device. Examples of such applications include: fleet management, smart metering, product tracking, home automation, e-health, etc.
MTC has great potential for being carried on wireless communication systems (also referred to here as mobile networks), owing to their ubiquitous coverage. However, for mobile networks to be competitive for mass machine-type applications, it is important to optimise their support for MTC. Current mobile networks are optimally designed for Human-to-Human communications, but are less optimal for machine-to-machine, machine-to-human, or human-to-machine applications. It is also important to enable network operators to offer MTC services at a low cost level, to match the expectations of mass-market machine-type services and applications.
To fully support these service requirements, it is necessary to improve the ability of mobile networks to handle machine-type communications.
Efforts have already been made in this direction, and the 3GPP Technical Report TR 23.888 “System Improvements for Machine-Type Communications”, hereby incorporated by reference, summarises an agreed architectural baseline for MTC services provided by a 3GPP wireless communication system.
According to this architectural baseline, the end to end application, between the MTC device and the MTC server, uses services provided by the 3GPP system. The 3GPP system provides transport and communication services (including 3GPP bearer services, IP Multimedia Subsystem or IMS, and Short Messaging Service or SMS) optimized for Machine-Type Communication.
In this architecture, each MTC Device connects to the 3GPP network (UTRAN, eUTRAN, etc.) via an MTCu interface. Each MTC Device communicates with a MTC Server or other MTC Devices using the 3GPP bearer services, SMS and IMS provided by the PLMN (Public Land Mobile Network). The MTC Server is an entity which connects to the 3GPP network via an MTCi interface (for IMS) or a MTCsms interface (for SMS) and thus communicates with MTC Devices. The MTC Server may be an entity outside of the operator domain, or inside an operator domain.
The above-mentioned interfaces are briefly described in the above document as follows:
MTCu: provides MTC Devices access to the 3GPP network for the transport of user plane and control plane traffic. The MTCu interface may be based on the Uu, Um, Ww and LTE-Uu interfaces.
MTCi: the reference point that the MTC Server uses to connect to the 3GPP network and thus communicate with MTC Device via 3GPP bearer services/IMS. MTCi may be based on Gi, Sgi, and Wi interfaces.
MTCsms: the reference point that the MTC Server uses to connect to the 3GPP network and thus communicate with MTC Device via 3GPP SMS.
The present invention relates to resource allocation in such an architecture. Before describing the specific problem addressed by the present invention, as well as its solution, some background explanation will first be given of the kinds of system to which the present invention may be applied.
As the present invention may be applied to various kinds of wireless communication system including UMTS and LTE, both of these types of system will be briefly outlined with reference to FIGS. 1 to 4. However, for the avoidance of doubt, it is noted that the present invention may also be applied to other types of wireless communication system including WiMAX (Worldwide Interoperability for Microwave Access) and GERAN (GSM EDGE Radio Access Network).
FIG. 2 shows the network topology in UMTS. A so-called UTRAN (UMTS Terrestrial Radio Access Network) 6 consists of one or more RNS (Radio Network Subsystem) 4. Each RNS controls the allocation and the release of specific radio resources to establish a connection between a Mobile Station MS 2 (also sometimes called UE (User Equipment)) and the UTRAN 6. The RNS 4 is responsible for the resources and transmission/reception in a group of cells.
In FIG. 2, the RNS 4 consists of a Node b 1, which connects wirelessly to each MS over a Uu interface, and a Radio Network Controller (RNC) 3 which is wirelessly connected to the Node b via a lub interface. The RNCs are in turn connected through a lu interface to a Serving GPRS Support Node (SGSN) 7 and a Gateway GPRS Support Node (GGSN) 8 for providing services to the users.
Over the radio interface Uu between the Mobile Station (MS) and the Radio Network System (RNS), user data traffic is transported using the User-Plane (that consists of Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC) and PHYsical (PHY) protocol layers. FIG. 1 shows the relationship between the protocol layers for the UMTS control plane and user plane.
The network topology in LTE is illustrated in FIG. 4. As can be seen, each UE 12 connects over a wireless link via a Uu interface to an eNB 11, and the network of eNBs is referred to as the eUTRAN 10.
Each eNB 11 in turn is connected by a (usually) wired link using an interface called S1 to higher-level or “core network” entities, including a Serving Gateway (S-GW 22), and a Mobility Management Entity (MME 21) for managing the system and sending control signalling to other nodes, particularly eNBs, in the network. In addition, a PDN or Packet Data Network Gateway (P-GW) is present, separately or combined with the S-GW 22, to exchange data packets with any packet data network including the Internet. The core network 20 is called the EPC or Evolved Packet Core.
Over the radio interface Uu between the User Equipment (UE) and the eNodeB, user data traffic is transported using the User-Plane consisting of PDCP, RLC, MAC and PHY protocol layers. FIG. 3 shows the relationship between the protocol layers for LTE control plane and user plane.
The concept of “bearers” is important for achieving quality-of-service (QoS) in a 3GPP-based network. In general, a “bearer” can be thought of as an information transmission path of defined capacity, delay and bit error rate, etc. so as to enable a given service or control function to be provided. Various types or levels of bearer can be established, the radio part being set up using radio resource control or RRC.
FIG. 7 shows an EPS Bearer Service Architecture proposed for LTE. The left side of the Figure represents the eUTRAN 10 with the EPC 20 occupying the middle part of the Figure. At the right-hand side, outside the LTE system as such, there is the Internet 24. The vertical bars represent the main entities in the user plane, from the UE 12 to eNB 11 through to S-GW 22 and P-GW 23, terminating in a peer entity (such as an Internet web server 25) connected to the P-GW 23. To provide an end-to-end service 40 between the UE 12 and Peer Entity 25 (as indicated by the upper horizontal band in the figure), the system sets up “bearers” as shown. An EPS Bearer 41 represents the entire connection within the LTE system; it constitutes a QoS flow for a particular service. The connection continues outside the LTE system via an External Bearer 42.
The EPS Bearer 41 is made up, in turn, of a radio bearer (RB) 51 over the link between the UE 12 and eNB 11, and an S1 Bearer 52 between the eNB 11 and S-GW 22. A further Bearer (S5/S8 Bearer 53) is set up between the S-GW 22 and P-GW 23. Each Bearer can be regarded as a “tunnel” in a given protocol layer for transport of packets, connecting the end points for the duration of a particular service or “session”, e.g. voice call or download. Thus, the radio bearer 51 transports the packets of the higher-layer EPS Bearer 41 between the UE 12 and eNB 11, and the S1 Bearer 52 transports the packets of the EPS Bearer 41 between the eNB 11 and S-GW 22. Bearer control through RRC, mentioned previously, includes the setting up of bearers for a particular session so as to ensure sufficient QoS, taking into account the resource situation in the eUTRAN 10 and existing sessions already in progress. It also involves the modification and release of RBs.
Radio Bearers include a Data Radio Bearer (DRB), generally used to carry user data but also sometimes signalling, and a Signalling Data Bearer (SRB) used for signalling. Radio bearers may be bidirectional (that is, defined on both uplink UL and downlink DL) or unidirectional (e.g., downlink only).
Radio Bearers typically remain defined for a relatively extended period of system operation (such as the duration of a voice call by a given UE). As such they persist over many cycles of operation in the system. A wireless communication system generally divides time into a succession of equal-length cycles or “frames”. Within each frame, transmission on the uplink and downlink may either occur successively (TDD) or simultaneously (FDD) depending on the system configuration. The length of each frame is related to a Transmission Time Interval (TTI) which is the time duration of one block of data transmitted in the system. Generally, a UE will transmit or receive one block at a time, except in the case of MIMO (Multiple-Input, Multiple-Output) where multiple antennas are employed.
In an LTE wireless communication system, the combination of protocol layers PDCP/RLC/MAC is also known as Layer 2, and the architecture for each of the downlink and uplink are depicted in FIGS. 5 and 6.
In these Figures, Service Access Points (SAP) for peer-to-peer communication are marked with circles at the interface between sublayers. The SAP between the physical layer and the MAC sublayer provides the transport channels. The SAPs between the MAC sublayer and the RLC sublayer provide the logical channels.
The multiplexing of several logical channels, i.e. radio bearers (RBs), on the same transport channel (i.e. transport block) is performed by the MAC sublayer. In both uplink and downlink, only one transport block is generated per TTI in the non-MIMO case.
FIG. 7 represents one possible structure for the PDCP sublayer. Each RB (i.e. DRB and SRB, except for SRB0) is associated with one PDCP entity. Each PDCP entity is associated with one or two (one for each direction) RLC entities depending on the RB characteristic (i.e. unidirectional or bi-directional) and RLC mode. The PDCP entities are located in the PDCP sublayer.
As already mentioned, Machine Type Communication (MTC) is a form of data communication which involves one or more entities that do not necessarily need human interaction. MTC is different to current communication models as it involves new or different market scenarios. Potentially it involves very large number of communicating entities (MTC devices) with little traffic per device. MTC devices may be required to access to the network simultaneously, and uplink traffic may exceed downlink traffic, for example where the MTC devices are required to send reports back to a supervising entity.
A typical UMTS network with MTC devices is shown in FIG. 9. Several MTC devices 100 are connected via radio interface MTCu to a Node b 1 that is controlled by a RNC 3. The user data for the MTC devices 100 is routed to the MTC server (not shown) via SGSN 4 and GGSN 5. Note that the Node b 1 and RNC 3 also serve normal MSs 2 at the same time, via the Uu interface.
Likewise, in the LTE network illustrated in FIG. 10, a group of MTC devices 200 is served by an eNB 11 which also maintains connections with normal UEs 12. The eNB receives signalling from the MME 21 and data (for example, a request for a status report from a supervisor of the MTC devices) via the S-GW 22.
Thus, based on current proposals, the MTCu interface is analogous to the Uu interface, and the MTC devices will be served in a similar way to normal user equipments by the mobile networks. When a large number of MTC devices connect to the same cell of a UMTS RNS or an LTE eNB, each of the devices will have the appropriate radio bearers configured to support the individual devices' applications although to a large extent each MTC device has little traffic.
As an example, we examine the bearer services for the MTC devices in an LTE network. In the MTCu interface, which is similar to the Uu interface mentioned earlier, an EPS bearer is one-to-one mapped to a data radio bearer (DRB), a DRB is one-to-one mapped to a Dedicated Traffic Channel (DTCH) logical channel, and all logical channels are many-to-one mapped to the Downlink or Uplink Shared Transport Channel (DL-SCH or UL-SCH). For each application of a MTC device, a DRB will be allocated, corresponding to the radio bearer 51 in FIG. 7. This involves a certain amount of control signalling for each RB and moreover, the available number of RBs is limited.
Therefore, an important issue is how to efficiently allocate radio resource to support a large number of MTC devices in the same cell while keeping to a minimum the control signalling overhead. Another important aspect is how to keep the minimum impact on other users (not machines) by the large number of machine-type communications.